The use of radioisotopes for various medical procedures such as brachytherapy and the like is well known. Such uses fall into two general categories: (i) high dose radioisotopes which are temporarily positioned in relation to a patient's body for a relatively short period of time to effect the radiation treatment, and (ii) low dose radioisotopes which are permanently implanted in a patient's body with the duration of the radiation treatment determined by the strength and half-life of the radioisotope being implanted. High dose radioisotopes are typically implanted using a catheter arrangement and a device commonly known as an afterloader that advances the high dose radioisotope located on the end of a source wire through the catheter to the desired location. Low dose radioisotopes, on the other hand, are implanted using an array of implant needles with the low dose radioisotopes being encapsulated in very small containers known as seeds that are manually loaded into a series of implant needles and then ejected to form a three-dimensional grid of radioisotopes in the patient that corresponds to a dose plan as determined by the physician. The goal of the low dose brachytherapy procedure is to position this three-dimensional grid of radioisotopes seeds in and around a target cancerous tissue area.
Each of the radioisotope seeds consists of a radioactive source such as Iodine (I-125) or Palladium (Pd-103) inside a small tube-like titanium shell that is about the size of a grain of rice. These type of low dose radioactive sources emit a very low energy radiation that is primarily absorbed by the tissue immediately surrounding the radioisotope seed. This constant low energy radiation is typically emitted by the radioisotope seeds for a period of up to six months as a way to kill the cancer cells in the target area without having to subject the patient to the discomfort and risks that often accompany high dose radioisotope procedures.
One common brachytherapy procedure is the use of low dose radioisotopes to treat prostate cancer. Although brachytherapy procedures using low dose radioisotopes can be applied to many different parts of the body, it is helpful to describe a particular treatment to gain a better understanding of these treatments. Currently, the typical prostate cancer brachytherapy procedure involves positioning a predetermined number of seeds (between 1-6) within each of a series of implant needles (up to 40), the seeds being spaced apart in each needle by small spacers. Typically, a small amount of bone wax is positioned on the tip of the implant needles to prevent the seeds and spacers from falling out until they are implanted in the patient. The loaded implant needles are then positioned at the appropriate location for insertion into the perineal area of the patient using a stand that has an X-Y coordinate grid. Each needle is manually positioned in the appropriate chamber in the grid and is inserted into the patient. An ultrasound probe is used to assist the physician in guiding each of the needles to the desired location. The seeds and spacers are delivered from the tip of the implant needle using a stylet and hollow needle arrangement where the hollow needle is preferably retracted while the stylet remains in place such that the seeds are forced out of the implant needle and such that the seeds occupy the space evacuated by the needle. When the brachytherapy procedure is completed, the implanted seeds form a three-dimensional grid of radioisotope sources that implements a predetermined dose plan for treating the prostate cancer in the patient. For a more detailed background of the procedures and equipment used in this type of prostate cancer treatment, reference is made to U.S. Pat. Nos. 4,167,179 and 6,537,192.
Following the removal of the implant needles and stylet, the seeds and spacer are no longer held in position relative to one another and an opportunity exists for them to migrate within and possibly outside of the tumor. Potential migration of the radioactive seeds within the body leads to several issues. First, the time consuming step of properly positioning the needles using the ultrasound probe is defeated. Secondly, migration of seeds results in a deviation from the treatment program possibly causing some areas of cancerous tissue to be overexposed to radiation while others are underexposed. Finally, migration of the seeds outside of the tumor can lead to the seeds becoming lodged within healthy tissue or organs, for example the lungs. The healthy tissue or organ is then exposed to radiation, which will have undesired effects on healthy cells. All of these potential consequences can contribute to reducing the overall success of the brachytherapy procedure.
In order to address the issues associated with migration of the radioactive seeds, a number of methods and devices have been developed to fix the orientation of the seeds and spacers within the tumor. Laboratory analysis indicates that the use of such configurations leads to an increase in the dosimetric quantifiers for implant adequacy as compared to procedures using loose seeds and spacers. Overall, the use of such configurations tends to lead to smaller prostate glands upon completion of treatment as compared to procedures using loose seeds and spacers.
Several methods for fixing the orientation of seeds and spacers include configurations in which the seeds and spacers are interlocked to create a unitary assembly, such as described in U.S. Pat. No. 6,010,446. In other configurations, the seeds and spacers are packaged in a carrier and subsequently placed into the tumor. Typically, these carriers are preloaded and shipped from an off-site location based on a treatment plan supplied by the treating physician. U.S. Pat. Nos. 4,697,575 and 4,815,449 describe a bioresorbable elongated member that carries a fixed number of multiple radioisotopes seeds. The member is heated to secure the relative positions of the seeds and spacers and make the elongated member sufficiently rigid so as to serve as the implanting needle. U.S. Pat. No. 5,460,592 describes a pre-loaded bioresorbable strand that is pre-loaded with ten seeds spaced at equal distances for use in a conventional metal implant needle and is commercially available under the Rapid Strand™ brand name. A physician uses a cutting jig during the brachytherapy procedure to cut each strand in order to provide the desired number of seeds to be loaded into the implant needle at a given treatment location. While the Rapid Strand™ strands have proven commercially successful, there are radiation exposure risks when cutting the strand if a seed is potentially nicked during the cutting process, in addition to limitations on the options of a physician in terms of dosage planning due to the pre-loaded nature of the strands. U.S. Pat. No. 6,264,600 describes a similar arrangement that uses a hollow suture member with multiple seeds and spacers preloaded into the suture member. Instead of heating the suture member or using a jig to cut the suture member, an open front end of the suture member is made long enough to extend past the tip of an implant needle and the tip of the implant needle is used as the guide for the physician to cut the suture member to the desired length prior to implant. U.S. Pat. Nos. 6,450,937 and 6,530,875 describe needle arrangements that utilize open ended and translucent needle carrier tubes as part of the loading process to permit visual inspection of the arrangement of seeds and spacers to be loaded, however, these needle carrier tubes are not intended to be implanted as part of the brachytherapy procedure. U.S. Pat. No. 6,679,824 describes a single stranded bioresorbable material that is preloaded with seeds by placing the seeds in slits made along the material and then preferably melting the material around each seed.
While the use of such fixed orientation seed and spacer configurations has lead to improvements in brachytherapy procedures for treating prostate cancer, the current configurations suffer in several areas. First, the use of interlocking seeds and spacers does not eliminate the potential for jamming within the insertion needle as they are advanced by an insertion stylet. Secondly, preloaded carriers do not provide physicians with any flexibility to alter the treatment program based on observations during the procedure. Thirdly, the cutting of carriers or sutures carries a risk of radiation exposure in the event that a seed is nicked during the cutting process. Finally, the preloaded nature of these carriers can lead to verification issues as the radiophysicist must still verify seed potency prior to use, thus requiring the removal of at least a portion of the preloaded carrier. It would be desirable to provide a seed carrier arrangement that offered the advantages of fixed orientation seed and spacer configurations while overcoming the problems and limitations presented by existing arrangements.